Rapid climate change at high latitudes is projected to increase wildfire extent in tundra ecosystems by up to fivefold by the end of the century. Tundra wildfire could alter terrestrial silica (SiO2) cycling by restructuring surface vegetation and by deepening the seasonally thawed active layer. These changes could influence the availability of silica in terrestrial permafrost ecosystems and alter lateral exports to downstream marine waters, where silica is often a limiting nutrient. In this context, we investigated the effects of the largest Arctic tundra fire in recent times on plant and peat amorphous silica content and dissolved silica concentration in streams. Ten years after the fire, vegetation in burned areas had 73% more silica in aboveground biomass compared to adjacent, unburned areas. This increase in plant silica was attributable to significantly higher plant silica concentration in bryophytes and increased prevalence of silica‐rich gramminoids in burned areas. Tundra fire redistributed peat silica, with burned areas containing significantly higher amorphous silica concentrations in the O‐layer, but 29% less silica in peat overall due to shallower peat depth post burn. Despite these dramatic differences in terrestrial silica dynamics, dissolved silica concentration in tributaries draining burned catchments did not differ from unburned catchments, potentially due to the increased uptake by terrestrial vegetation. Together, these results suggest that tundra wildfire enhances terrestrial availability of silica via permafrost degradation and associated weathering, but that changes in lateral silica export may depend on vegetation uptake during the first decade of postwildfire succession.
Climate change is creating widespread ecosystem disturbance across the permafrost zone, including a rapid increase in the extent and severity of tundra wildfire. The expansion of this previously rare disturbance has unknown consequences for lateral nutrient flux from terrestrial to aquatic environments. Lateral loss of nutrients could reduce carbon uptake and slow recovery of already nutrient‐limited tundra ecosystems. To investigate the effects of tundra wildfire on lateral nutrient export, we analyzed water chemistry in and around the 10‐year‐old Anaktuvuk River fire scar in northern Alaska. We collected water samples from 21 burned and 21 unburned watersheds during snowmelt, at peak growing season, and after plant senescence in 2017 and 2018. After a decade of ecosystem recovery, aboveground biomass had recovered in burned watersheds, but overall carbon and nitrogen remained ~20% lower, and the active layer remained ~10% deeper. Despite lower organic matter stocks, dissolved organic nutrients were substantially elevated in burned watersheds, with higher flow‐weighted concentrations of organic carbon (25% higher), organic nitrogen (59% higher), organic phosphorus (65% higher), and organic sulfur (47% higher). Geochemical proxies indicated greater interaction with mineral soils in watersheds with surface subsidence, but optical analysis and isotopes suggested that recent plant growth, not mineral soil, was the main source of organic nutrients in burned watersheds. Burned and unburned watersheds had similar δ15N‐NO3−, indicating that exported nitrogen was of preburn origin (i.e., not recently fixed). Lateral nitrogen flux from burned watersheds was 2‐ to 10‐fold higher than rates of background nitrogen fixation and atmospheric deposition estimated in this area. These findings indicate that wildfire in Arctic tundra can destabilize nitrogen, phosphorus, and sulfur previously stored in permafrost via plant uptake and leaching. This plant‐mediated nutrient loss could exacerbate terrestrial nutrient limitation after disturbance or serve as an important nutrient release mechanism during succession.more » « less
- NSF-PAR ID:
- Publisher / Repository:
- Date Published:
- Journal Name:
- Global Change Biology
- Medium: X Size: p. 1408-1430
- ["p. 1408-1430"]
- Sponsoring Org:
- National Science Foundation
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